#!/usr/bin/perl -w
#
# Copyright (C) 2008 Rien Broekstra <rien@rename-it.nl>
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; version 2 dated June,
# 1991.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
#
#
# Configuration variables:
#
#       conffile     - path to dhcpd's configuration file (default "/etc/dhcpd.conf")
#       leasefile    - path to dhcpd's leases file (default "/var/lib/dhcp/dhcpd.leases")
#

use POSIX;
use Time::Local;
use Sys::Hostname;
use strict;

my $CONFFILE = exists $ENV{'conffile'} ? $ENV{'conffile'} : "/etc/dhcpd.conf";
my $LEASEFILE = exists $ENV{'leasefile'} ? $ENV{'leasefile'} : "/var/db/dhcpd.leases";

my (@activeleases, %dhcp_pools, $pool_start, $pool_end, $pool_size, $pool_free, $pool_usage, $pool_status, $label, $lease, @output);
my $hostname = hostname;

# Determine all leased IP addresses
@activeleases = determine_active_leases();

# Determine the available IP pools
%dhcp_pools = determine_pools();

# For each pool, count how many leases from that pool are currently active
foreach $pool_start (keys %dhcp_pools) {
    $pool_size = $dhcp_pools{$pool_start};
    $pool_end = $pool_start+$pool_size-1;
    $pool_free = $pool_size;

    foreach $lease (@activeleases) {
        if ($lease >= $pool_start && $lease <= $pool_end) {
    		$pool_free--;
        }
    }

    $label = ip2string($pool_start)."_".ip2string($pool_end);
    $pool_usage = sprintf("%.1f", 100*($pool_size-$pool_free)/$pool_size);

    push(@output, "PUTVAL $hostname/dhcp_pool/gauge-$label N:$pool_usage\n");
}

print @output;
exit 0;

################
###### FUNCTIONS 

# Parse dhcpd.conf for range statements.
#
# Returns a hash with start IP -> size
sub determine_pools {
    my (%pools, @conffile, $line, $start, $end, $size);

    open(CONFFILE, "<${CONFFILE}") || exit -1;
    @conffile = <CONFFILE>;
    close (CONFFILE);

    foreach $line (@conffile) {
	next if $line =~ /^\s*#/;

	if ($line =~ /range[\s]+([\d]+\.[\d]+\.[\d]+\.[\d]+)[\s]+([\d]+\.[\d]+\.[\d]+\.[\d]+)/) {
	    $start = string2ip($1);
	    $end = string2ip($2);

	    defined($start) || next;
	    defined($end) || next;

            # The range statement gives the lowest and highest IP addresses in a range.
	    $size = $end - $start + 1;

	    $pools{$start} = $size;
	}
    }
    return %pools;
}

# Very simple parser for dhcpd.leases. This will break very easily if dhcpd decides to
# format the file differently. Ideally a simple recursive-descent parser should be used.
#
# Returns an array with currently leased IP's
sub determine_active_leases {
    my (@leasefile, $startdate, $enddate, $lease, @activeleases, $mytz, $line, %saw);

    open(LEASEFILE, "<${LEASEFILE}") || exit -1;
    @leasefile = <LEASEFILE>;
    close (LEASEFILE);

    @activeleases = ();

    # Portable way of converting a GMT date/time string to timestamp is setting TZ to UTC, and then calling mktime()
    $mytz = $ENV{'TZ'};
    $ENV{'TZ'} = 'UTC 0';
    tzset();

    foreach $line (@leasefile) {
	if ($line =~ /lease ([\d]+\.[\d]+\.[\d]+\.[\d]+)/) {
	    $lease = string2ip($1);
	    defined($lease) || next;

	    undef $startdate;
	    undef $enddate;
	}
	elsif ($line =~ /starts \d ([\d]{4})\/([\d]{2})\/([\d]{2}) ([\d]{2}):([\d]{2}):([\d]{2})/) {
	    $startdate = mktime($6, $5, $4, $3, $2-1, $1-1900, 0, 0);
	}
	elsif ($line =~ /ends \d ([\d]{4})\/([\d]{2})\/([\d]{2}) ([\d]{2}):([\d]{2}):([\d]{2})/) {
	    $enddate = mktime($6, $5, $4, $3, $2-1, $1-1900, 0, 0);
	}
	elsif ($line !~ /abandoned/) {
	    if (defined($enddate) && defined($startdate) && defined($lease)) {
		if ($startdate < time() && $enddate > time()) {
		    push (@activeleases, $lease);
		}
	    }
	}

    }

    # Set TZ back to its original setting
    if (defined($mytz)) {
	$ENV{'TZ'} = $mytz;
    }
    else {
	delete $ENV{'TZ'};
    }
    tzset();

    # Sort the array, strip doubles, and return
    return grep(!$saw{$_}++, @activeleases);
}

#
# Helper routine to convert an IP address a.b.c.d into an integer
#
# Returns an integer representation of an IP address
sub string2ip {
    my $string = shift;
    defined($string) || return undef;
    if ($string =~ /([\d]+)\.([\d]+)\.([\d]+)\.([\d]+)/) {
	if ($1 < 0 || $1 > 255 || $2 < 0 || $2 > 255 || $3 < 0 || $3 > 255 || $4 < 0 || $4 > 255) {
	    return undef;
	}
	else {
	    return $1 << 24 | $2 << 16 | $3 << 8 | $4;
	}
    }
    return undef;
}

#
# Returns a dotted quad notation of an
#
sub ip2string {
    my $ip = shift;
    defined ($ip) || return undef;
    return sprintf ("%d.%d.%d.%d", ($ip >> 24) & 0xff, ($ip >> 16) & 0xff, ($ip >> 8) & 0xff, $ip & 0xff);
}